Exoplanet Search Techniques: Overview. PHY 688, Lecture 28 April 3, 2009

Transcription

1 Exoplanet Search Techniques: Overview PHY 688, Lecture 28 April 3, 2009

2 Course administration final presentations Outline see me for paper recommendations 2 3 weeks before talk see me with draft of presentation 1 week before talk midterm exam discussion Review of previous lecture exoplanet search techniques: direct imaging Exoplanet search techniques (continued) comparison of sensitivities April 3, 2009 PHY 688, Lecture 28 2

3 Hydrogen Phase Diagram Hydrogen phase diagram (From Lecture 14) T ρ 0.67 T T ρ 0.4 T ρ 0.67 Midterm Problem 1 (Burrows & Liebert 1993) April 3, 2009 PHY 688, Lecture 28 3

4 Lecture 25: Radii of Very Hot Jupiters some large radii cannot be explained by coreless planet models with high-altitude stratospheres: extra internal power source? stratospheric heat trap tidal heating damping or orbital eccentricity and apparent resetting of planet age? host stars are giga-years old (Fortney et al. 2007) Midterm Problem 2: Transit Radius Effect April 3, 2009 PHY 688, Lecture 28 4

5 From Lecture 22: Exoplanet Transit Spectroscopy From Star To Observer Planet X A ray may be wholly, partly, or negligibly absorbed, depending upon its impact parameter and its wavelength. Thus, the planet appears larger when observed at wavelengths that are strongly absorbed. Midterm Problem 2: Transit Radius Effect April 3, 2009 PHY 688, Lecture 28 5

6 From Lecture 11: Luminosity (i.e., Surface Gravity) Effects at A0 Midterm Problem 3: Young and Old Brown Dwarfs (figure: D. Gray) April 3, 2009 PHY 688, Lecture 28 6

7 From Lecture 11: Gravity-Sensitive Features in UCDs Midterm Problem 3: Young and Old Brown Dwarfs April 3, 2009 PHY 688, Lecture 28 7 (McGovern et al. 2004)

8 From Lecture 11: Gravity in UCDs Key species: neutral alkali elements (Na, K) weaker at low g hydrides CaH weaker at low g FeH unchanged oxides VO, CO, TiO stronger at low g H 2 O ~ unchanged Midterm Problem 3: Young and Old Brown Dwarfs (Kirkpatrick et al. 2006) Wavelength (µm) April 3, 2009 PHY 688, Lecture 28 8

9 Course administration final presentations Outline see me for paper recommendations 2 3 weeks before talk see me with draft of presentation 1 week before talk midterm exam discussion Review of previous lecture exoplanet search techniques: direct imaging Exoplanet search techniques (continued) comparison of sensitivities April 3, 2009 PHY 688, Lecture 28 9

10 Previously in PHY 688 April 3, 2009 PHY 688, Lecture 28 10

11 From Lecture 2: Detection Techniques for Substellar Objects brown dwarfs precision radial velocity monitoring periodic Doppler shift of host star spectrum due to planet s gravitational pull resolved imaging of binary systems seeing-limited, speckle interferometry, adaptive optics unresolved photometry of hot stars e.g., cool infrared excess in an otherwise much hotter white dwarf large-area sky surveys extremely red objects exoplanets precision radial velocity monitoring pulsar timing apparent periodicity in pulsar rotation period due to planet s gravitational pull transit photometry ~1% dimming of star due to planet passing in front microlensing gravitational lensing of light from background stars resolved imaging! extremely high-contrast adaptive optics April 3, 2009 PHY 688, Lecture 28 11

12 Planet Detection Methods (statistics as of Oct 2007) (Perryman 2000) April 3, 2009 PHY 688, Lecture 28 12

13 Planet Detection History 318 radial velocity 58 transits 8 microlensing 7 pulsar timing 4 (11) imaging April 3, 2009 PHY 688, Lecture 28 13

14 Planet Detection: Direct Imaging 2MASS B ~ 5 M Jup primary is a young (~10 Myr) brown dwarf discovered with adaptive optics (AO) on the 8 m Very Large Telescope (VLT) (Chauvin et al. 2004) April 3, 2009 PHY 688, Lecture 28 14

15 Challenge of Direct Imaging: In the visible near-ir F Sun / F Earth ~ 10 9 F Sun / F Jup ~ 10 8 challenging wavefront control small PSF can observe from the ground In mid-ir F Sun / F Earth ~ 10 6 F Sun / F Jup ~ 10 4 easier wavefront control >10 larger PSF need to observe from space Star-Planet Contrast April 3, 2009 PHY 688, Lecture 28 15

16 Challenge of Direct Imaging: Keck AO speckles at 2.2 µm Star-Planet Contrast 2M 1207 B (~5 M Jup ) r = 1 high angular resolution, high-contrast imaging suffers from wavefront aberrations or order ~ λ aberrations manifested as speckles of size ~ λ/d speckles pose as fake planets d exoplanets HR 8799 b,c,d (~10 15 M Jup ) c b (Kalas 2005) April 3, 2009 PHY 688, Lecture 28 16

17 Planet Detection: Imaging state of the art: contrast of 9 mag at 0.5", 11 mag at 1" in the near-ir benefits: can perform atmospheric spectroscopy limitations: hot (young), well-separated (>0.5") planets no mass, radius information false positives: telescope speckles, distant background stars April 3, 2009 PHY 688, Lecture 28 17

18 Course administration final presentations Outline see me for paper recommendations at least 2 weeks before talk see me with draft of presentation 1 week before talk midterm exam discussion Review of previous lecture exoplanet search techniques: direct imaging Exoplanet search techniques (continued) comparison of sensitivities April 3, 2009 PHY 688, Lecture 28 18

19 Planet Detection: Precision Radial Velocity (Doppler Spectroscopy) (Johnson et al. 2006) April 3, 2009 PHY 688, Lecture 28 19

20 Planet Detection: Precision Radial Velocity (Doppler Spectroscopy) (Johnson et al. 2006) April 3, 2009 PHY 688, Lecture 28 20

21 Planet Detection: Precision Radial Velocity (Doppler Spectroscopy) stellar spectrum April 3, 2009 PHY 688, Lecture 28 21

22 Planet Detection: Precision Radial Velocity (Doppler Spectroscopy) stellar spectrum with I 2 lines superposed: I 2 allows precise wavelength calibration April 3, 2009 PHY 688, Lecture 28 22

23 Planet Detection: Precision Radial Velocity (Doppler Spectroscopy) state of the art: m/s precision HF or iodine cell dual optical fiber (one looking at target star, one at ThAr calibration source) benefits: orbital solution modulo sin i limitations: sin i ambiguity; radius, atmospheric composition unknown false positives: star spots, pulsations April 3, 2009 PHY 688, Lecture 28 23

24 1 0 Planet Detection: Astrometry y (mas) x (mas) (Benedict et al. 2006) April 3, 2009 PHY 688, Lecture 28 24

25 Planet Detection: Astrometry state of the art: ~0.05 mas precision benefits: exact orbital solution, dynamical mass limitations: gets harder with heliocentric distance (>20 pc) planet radius, atmospheric composition unknown false positives: star spots April 3, 2009 PHY 688, Lecture 28 25

26 Planet Detection: Transits HD b was a known extrasolar planet in a = AU semi-major axis April 3, 2009 PHY 688, Lecture (Charbonneau et al. 2000)

27 Planet Detection: Transits April 3, 2009 PHY 688, Lecture 28 27

28 Planet Detection: Transits "F max F # $ R ' P & ) % ( duration # R S 2 $ #10 *2 R P R S & % R Jup R Sun R S 2+a P #14 hr $ R S & % R Sun ' ) ( 2 ' $ P ' )& ) (% 11 yr ( 1 3 #1.3 hr $ probability # 0.1% R S R Sun ' $ & ) #10% R S R Sun ' & ) % a 5 AU( % a 0.05 AU( $ & % R S R Sun ' $ P ' )& ) (% 3 days( 1 3 state of the art: 0.1% photometry benefits: full orbital solution, temperature, radius, more! limitations: close-in planets (hot Jupiters) false positives: F-M star binaries, grazing eclipses of stars, triple stars with eclipses April 3, 2009 PHY 688, Lecture 28 28

29 Planet Detection: Pulsar Timing 98.2-day periodicity subtracted (Wolszczan & Frail 1992) 66-day periodicity subtracted PSR pulse shape, 430 MHz rotational period: ± s (10 14 s) both periodicities subtracted April 3, 2009 PHY 688, Lecture 28 29

30 The Pulsar Planets only one more pulsar planet known: around PSR B very different from the original pulsar planetary system planet orbits a close neutron star white dwarf binary a p = 23 AU M p = 2.5±1 M Jup April 3, 2009 PHY 688, Lecture (Wolszczan 2008)

31 Pulsar Timing: Non-Keplerian Orbital Motions residuals of standard pulsar timing model; no planets residuals including Keplerian orbits for 3 planets residuals including non-keplerian resonant (3:2) interactions between planets B and C April 3, 2009 PHY 688, Lecture (Konacki & Wolszczan 2003)

32 Pulsar Timing state of the art: s pulsar timing precision s residuals after orbital fits benefits: very high sensitivity to mass: ~10 2 M Earth ~ M Moon most sensitive technique to date! full orbital solution limitations: few pulsars known, planet radius, atmospheric composition unknown false positives: pulsar position needs to be known precisely (<0.1") first reported pulsar planets (1991) were retracted April 3, 2009 PHY 688, Lecture 28 32

33 Planet Detection: Gravitational Microlensing April 3, 2009 PHY 688, Lecture 28 33

34 Planet Detection: Gravitational Microlensing to be presented in more detail by Dharmesh on May 8! April 3, 2009 PHY 688, Lecture 28 34

35 Planet Detection Techniques: Comparison direct imaging habitable zone ~150 planets detected as of mid-2004: r.v. (blue) transits (red) microlensing (yellow) pulsar timing (purple) sample ~doubled by 2009 added 5 through direct imaging (magenta, at >20AU) April 3, 2009 (LawsonPHY et al. 2004) 688, Lecture 28 35

36 Planet Detection Techniques: Comparison direct imaging Super-Jupiters (>1 MJup) r.v., astrometry, transits, pulsar timing, microlensing, direct imaging Jupiters, Neptunes, Super-Earths (>0.01 MJup 3 MEarth) r.v., astrometry, transits, pulsar timing, microlensing lowest mass r.v. planet: Msini = 4.2 MEarth lowest mass microlensing planet: M = 3.3 MEarth orbits a brown dwarf Earths pulsar timing to be detected through transits by Kepler Lunar/Mercury-mass (0.02 MEarth) planet pulsar timing April 3, 2009 (LawsonPHY et al. 2004) 688, Lecture 28 36